Gravitational infall in the hard wall model

TL;DR

This paper studies how scalar shells in a holographic confining model either collapse into black branes or oscillate indefinitely, revealing states that do not thermalize in the dual field theory.

Contribution

It introduces a detailed analysis of scalar shell dynamics in the hard wall model, showing conditions for non-thermalizing oscillations and providing an analytic proof that black branes cannot form in certain regimes.

Findings

Oscillating scalar shells persist indefinitely without forming black branes.

The scalar operator expectation value exhibits sustained oscillations with modulated amplitude.

Certain initial conditions lead to non-thermalizing states in the dual field theory.

Abstract

An infalling shell in the hard wall model provides a simple holographic model for energy injection in a confining gauge theory. Depending on its parameters, a scalar shell either collapses into a large black brane, or scatters between the hard wall and the anti-de Sitter boundary. In the scattering regime, we find numerical solutions that keep oscillating for as long as we have followed their evolution, and we provide an analytic argument that shows that a black brane can never be formed. This provides examples of states in infinite-volume field theory that never thermalize. We find that the field theory expectation value of a scalar operator keeps oscillating, with an amplitude that undergoes modulation.